1. Field of the Invention
This invention relates in general to propulsion systems, and in particular to fuels for pulse detonation engines that may be used for flight vehicles.
2. Description of Related Art
A pulse detonation engine (PDE) is an apparatus which produces a high temperature and high pressure exhaust gas from a series of repetitive detonations within a detonation chamber to generate thrust at supersonic speeds for flight vehicles, such as aircraft, missile or spacecraft. At high speeds, such as Mach 2 to about Mach 3.5, a PDE would theoretically be more efficient than conventional turbojets because such engine does not require compressors or turbines. As a result, a PDE would theoretically weigh less that a conventional gas turbine engine that supplies an equivalent amount of thrust.
In a PDE, a highly explosive fuel is mixed with an oxidant and ignited to create an initial detonation wave. The detonation shock releases substantial amounts of heat and energy that compresses the gas mixture, thereby increasing its pressure, density and temperature. As the wave propagates toward an open rearward end of the detonation chamber, thrust is produced. The detonation chamber is purged of the detonation or exhaust gases and the cycle is then repeated.
Heretofore, the highly explosive fuels employed in a PDE are conventional gases, such as hydrogen or propane, or conventional atomized aircraft fuels, such as JP-10. When such conventional fuels are used, oxygen is often required as an oxidant to create an initial detonation wave shortly after ignition. For many of the conventional fuels used in present pulse detonation engines, it has not been possible to create a detonation wave with air only. When the spark is ignited, the detonation wave does not immediately form, but takes several inches or feet before the detonation wave forms. That distance is known as the transition length. The safest application to minimize the transition length is MAPP gas. If the transition length is minimized using MAPP gas and either air or oxygen, thrust is maximized. There is a need for a PDE fuel which may create an initial detonation wave with air alone.
It has been discovered that a highly energetic liquid hydrocarbon mixture which contains methylacetylene-propadiene, commonly referred to as MAPP gas (hereinafter referred to as MAPP gas), meets this need.
The MAPP gas fuel of this invention contains methylacetylene-propadiene. The MAPP gas fuel may be used alone as a fuel for a pulse detonation engine or it may be combined with other conventional fuels such as hydrogen, JP-4, JP-5, JP-10, kerosene or a hydrocarbon containing fuel. Such hydrocarbon containing fuel includes, but is not limited to, acetylene, methane, ethylene, propane, butane or liquified petroleum gas.
This invention also includes a method of powering a flight vehicle having a pulse detonation engine which includes the following steps: supplying a MAPP gas fuel and an oxidant to a detonation chamber of a pulse detonation engine to form a detonable mixture; and igniting the detonable mixture in the detonation chamber to create a propagating detonation wave of detonation or exhaust gases in the chamber. The method also includes purging the detonation or exhaust gases from the detonation chamber, then repeating these steps.
In a preferred embodiment of this invention, a flight vehicle having a pulse detonation engine includes the following: a tank of MAPP gas fuel; a source of oxidant; a detonation chamber in fluid communication with the tank of MAPP gas fuel and the oxidant source, the chamber structured to propagate a detonable wave of gases when a mixture of MAPP gas fuel and oxidant is ignited; and an ignitor in communication with the detonation chamber for igniting the detonable mixture.